Alloy steel



Nov. 14, 1961 4 J. L. HURLEY ETAL 3,008,820

" ALLOY STEEL Filed May 11. 1959 o 'I'IHMXOOH sszmaavn JOHN LYONS HURLEY' THOMAS NEWTON ARMSTRONG Jr.

INVENTOR5 fh 4am ATTORNEY United States Patent The present invention relates to alloy steels, and, more particularly, to air hardenable alloy steels of low alloy content and characterized by a combination of desired metallurgical properties, especially yield strengths above certain limits upon tempering at or above certain minimum temperatures the alloy steels being especially suitable for use in the manufacture of tubular articles, e.g.,

oil well casings, and in other various industrial and commercial applications.

As is known to those skilled in the art, new and improved alloy steels are continually required to replace prior art steels no longer capable of satisfying the increasingly severe demands of many industrial and commercial applications. To illustrate, the petroleum industry is of necessity being forced to drill deeper and deeper wells in order to reach reservoirs of oil. Depths of over 23,000 feet have been reached and it is not uncommon to drill to a depth exceeding 15,000 feet. As would be expected, these deep wells require steels, e.g., for casings, capable of manifesting a combination of mechanical prop erties including strength, ductility, toughness, etc., superior to those manifested by steels used hitherto. It can be appreciated that the cost of repairing casing failure is substantial and would rise sharply as the depth of the well increased. Other segments of industry are confronted with similar difiiculties. An additional problem is brought about by the fact that superior alloy steels are needed which are of low cost.

One of the more important reasons prior art alloy steels in commercial use, for example, as tubular articles, are unsatisfactory is that they lack sufficient yield strength, i.e., 150,000 p.s.i. or higher at 0.2% offset, to support the heavy loads to which they are subjected. For example, steel oil well casings required to withstand high bottom hole pressures and to support the high tensile loads resulting from the longer lengths of easing required to reach the bottom of such deep wells. There are presently available alloy steels of relatively high hardenability, e.g., AISI 4340 steel, which can develop suitable yield strength properties provided they are liquid quenched, e.g., water quenched or oil quenched, from austenitizing temperatures before tempering. However, there is reluctance to, for example, water quench tubular articles made from steels of relatively high hardenability because of the inherent dangers associated with quench cracking. Water quenching, being a severe quench, presents certain hazards as is well known and, as a consequence thereof, rigid inspection procedures must be employed and commercial necessity requires this testing to be nondestructive. Further, it is nearly impossible as a practical matter to satisfactorily water quench alloy steel tubular articles because of the problems created as a result of the warping or distortion which occurs due to the high internal stresses set up in the quenched article. A distorted article, assuming it did not have to be scrapped, would normally require the application of straightening techniques to prepare the article for service, but even such techniques are causative of induced residual stresses. It follows that it would be desirable to avoid such tedious and costly procedures while providing low cost alloy steels of properties required in service.

The problem is further complicated when it is considered that various industrial applications desire alloy steels ice tempered at or above a specified temperature. For example, the petroleum industry prefers for easing manufacture that the tempering operation be carried out at 1000" F. and above in order that the alloy steel be characterized by low residual stress values. Heat treatments prior to tempering, inter alia, are causative of inducing internal stresses in the alloy steel and such stresses render the steel susceptible to subsequent failure, e.g., as by stress corrosion cracking, in use. Too, residual stresses may be additive to applied stresses and thus cause failure at a lower applied stress than would normally be expected. Alloy steels such as AISI 4340 have been used in the air-hardened and tempered condition for various purposes but their yield strength in this condition of heat treatment does not reach a magnitude of 150,000 p.s.i., if tempered at 1000 F. or higher.

It has now been discovered that a low cost alloy steel of special composition and of low alloy content can be provided which possesses a combination of desired properties which enables the new alloy steels to be used in sundry industrial and commercial applications. The alloy steels of the invention do not require a liquid quenching treatment, e.g., a water or oil quenching treatment and, thus, problems common to and associated with liquid quenching, e.g., distortion and cracking, are avoided. Moreover, the alloy steels of the present invention manifest a highly satisfactory combination of mechanical properties including high tensile and yield strengths, toughness, good ductility, etc., in the air-hardened and tempered condition which makes the alloy steels eminently suitable for use in the production of tubular articles.

It is an object of the present invention to provide alloy steels of low alloy content characterized by a combination of good mechanical properties including high yield and tensile strengths, good ductility, toughness, etc., thus making the alloys suitabe for diversified use.

Another object of the invention is to provide alloy steels of high yield strength and of low alloy content for use in the production of tubular articles, e.g., steel oil well casings to be used in deep wells.

The invention also contemplates providing alloy steels capable of affording a 0.2% offset yield strength of at least 150,000 p.s.i. when in the normalized-tempered condition, the tempering being carried out at temperatures of 1000 F. or more.

Other objects and advantages will become apparent from the following description, taken in conjunction with the accompanying drawing in which theaccompanying figure depicts curves relating temperatures of tempering to hardness of an alloy steel contemplated within the scope of the invention and the well known AISI 4340 alloy steel.

Generally speaking, the present invention contemplates providing alloy steels of special composition and of low alloy content which are characterized by toughness, good ductility and high strength properties, e.g., yield strengths above 150,000 p.s.i. at 0.2% offset in the air-hardened condition, thus making the new alloy steels particularly suitable for use, inter alia, in the manufacture of tubular articles such as oil well casings for use in deep wells. In accordance with the invention, a highly satisfactory combination of mechanical properties is achieved with alloy steels of the following preferred composition: about 0.35% to about 0.45% carbon, about 1.3% to about 1.6% manganese, about 0.2% to about 0.4% silicon, about 1% to about 1.5% nickel, about 0.8% to about 1.2% chromium, about 0.25% to about 0.35% molybdenum, the balance being essentially iron. It is advantageous and further preferred that vanadium in an amount of up to about 0.1%, e.g., 0.05%, be present in the alloys having compositions as above set forth. Vanadium promotes grain size refinement in the alloy steels and when in solution imparts increased hardenability properties to the steels. Further, it resists adverse influences of high tempering temperatures, i.e., it resists the lowering of strength properties attributable to tempering treatment. Thus, higher tempering temperatures can be employed than otherwise might be the case.

It has been found that alloy steels having compositions within the foregoing ranges manifest in the normalized and tempered condition a 0.2% ofiset yield strength well above 150,000 pounds per square inch (p.s.i.), e.g., over 165,000 p.s.i., even when tempering is conducted at temperatures of 1000 F. or more. This high strength level is attained while achieving good ductility and toughness. Thus, the alloy steels are especially suitable for use as oil well casing, particularly for service in deep wells of depths of 15,000 feet or more, e.g., 20,000 feet. Moreover, the combination of desired properties enables the alloy steels to be used in many other applications requiring low cost steels of good all-around properties particularly in the normalized and tempered condition. Satisfactory results are also obtained with alloy steels of the invention containing about 0.3% to about 0.6% carbon, about 1.3% to about 1.8% manganese, about 0.15% to about 0.6% silicon, about 0.5% to about 2.25% nickel, about 0.7% to about 1.5% chromium, about 0.2% to about 0.4% molybdenum, up to 0.1% vanadium, balance essentially iron. Sulfur and phosphorus, if present, each should not exceed 0.05% 'by weight of the alloys.

Other beneficial characteristics and advantages of the alloy steels of the invention result from the fact they do not require water or oil quenching treatments in order to develop the desired properties for use as tubular articles, e.g., oil well casings. This factor, as referred to hereinbefore, eliminates tedious problems associated with water quenching and tends to economic losses brought about by quench cracking, etc. In addition, the alloy steels of the invention lend themselves readily to tempering treatments carried out above 1000 F., a treatment, as indicated hereinbefore, desired for certain applications.

The carbon content of the alloy steels should not fall below 0.3% and preferably not below 0.35%. Too little carbon adversely lowers the hardenability characteristics of the steels and excessive amounts of carbon detract from the toughness of the steels. Manganese has a strong positive effect upon hardenabilitv in the alloy steels of the invention and amounts less than about 1.3% would lessen this efiect. Too much manganese reduces the toughness of the steels and also promotes the retention of austenite after cooling. It is preferred that the manganese content of the steels not exceed 1.6%. Both nickel and chromium increase the hardenability of the alloy steels. Further, nickel increases the toughness of the steels and chromium resists softening during tempering. Nickel should be present in amounts of at least about 1% as otherwise both hardenability and toughness are impaired. The chromium content should not be less than 0.7% for best results and preferably should not exceed 1.2%. Molybdenum increases hardenability considerably, resists softening during tempering and also counteracts temper brittleness development. At least 0.2%, preferably at least 0.25%, molybdenum should be present in the new alloy steels of the invention. Silicon is employed primarily to insure adequate deoxidation.

4 ing at 102$ F. or 1050 F. for about 1 hour has been found to give very satisfactory results.

For the purpose of giving those skilled in the art a better understanding of the invention and/or a better appreciation of the advantages of the invention, the following illustrative example is given:

EXAMPLE I An alloy steel within the invention, referred to as Alloy A for convenience, and the well known A181 4340 steel, the composition of which is outside of the invention,

were forged to two inch squares and then the bottom portion of each was forged to a 1% inch diameter bar. (Bars of 1% inches diameter have roughly the same cooling rate as the upset end of the thickest oil well casing which has a wall thickness of about one inch.) The alloys were austenitized at 1600 F. for 1 hour and then air-cooled. Alloy A was then temperated for 1 hour at 1050' F. and the A181 4340 steel was tempered at 1025 F. for 1 hour. The steels were also subjected to a series of tempering treatments which were carried out by holding the time constant and varying the temperature (about 1000 F., 1050 F. and 1150 F.), the results of which in terms relating to hardness are shown graphically in FIG.-

1. The chemical compositions of the two alloys are given in Table I below and the strength and other mechanical properties of the two specimens of each of the alloys are given in Table II.

Table l Per- Per- Per- Per- Per- Per- Per- Alloy cent cent cent cent cent cent cent 0 Mn. Si Ni Or Mo V Table II MECHANICAL PROPERTIES 1 Tem- Ofl'set Elongred Yield Tensile gation Redne- Alloy ard- Strength Strength in 1.4 tion of (gees; (10i (101 inch, t is,

ac p.s. .s. 1 percen rcen well 0 0.2% D De 41.4 175.1 192.4 16.4 47.0 as 1%? s: 3017 11917 14810 18:6 5219 l Tensile specimens were of 0.375 inch diameter. 8 Tempered 1 hour at 1050 F. I Tempered 1 hour at 1025 F.

The data of Table H and FIG. 1 illustrate that the Alloy A of the present invention affords a satisfactory combination of properties including high yield and tensile strengths and satisfactory hardness. That the alloy steels within the invention possess a high degree of duetility at high strength levels is shown by the elongation and reduction of area data of Alloy A in Table II. In using standard V-notch Charpy testing procedures (10 x 10 x mm., 45'' notch, 2 mm. deep and 0.25 mm. radius) Alloy A exhibited impact strengths of 16, 10 and 5 foot pounds at 100F., 20 F. and 100 F., respectively. Such results compare favorably with the impact strengths of about 15, 7 and 4 foot pounds, respectively,

In c g the invention into practice, the austenifizing which were found for the A181 4340 steel at the same or above e.g., up to 1250 F. can be employed. Temper- 75 temperatures. Thus, alloy steels of the invention also possess, in combination with high strength, a good degree of toughness (further evidenced by the elongation and reduction-of area data of Table II).

The alloy steels of the present invention can be used for numerous applications and are particularly useful in the production of tubular articles. The fact that the alloys of the invention possess a yield strength in excess of 150,000 p.s.-i. after tempering at 1000 F. or above and do not a water quench, renders such alloys eminently suitable for use in the manufacture of oil well steel casings. Furthermore, the alloy steels of the invention because of good all-around properties in the normalized-tempered condition are su-itable'for use in the form of high-pressure pipe lines, tubing, machinery components, engineering structures including the transportation field, and in general where applications require alloy steel articles of high strength and good ductility but because of the geometry thereof it would not be practical to subject the article to liquid quenching treatments.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. For example, the alloy steels of the invention can be used for applications where liquid quenching treatments can be employed. Such modifications and variations are considered to be within the purview and scope of the invention and appended claim.

An air hardened alloy steel characterized when normalized and thereafter tempered at a temperature of at least 1000" F. by a combination of mechanical properties including good ductility, impact resistance and a yield strength of at least 150,000 p.s.i. at 0.2% olfset, thus rendering the alloy steel particularly suitable for use in the production of tubular articles, said alloy steel consisting essentially of about 0.35% to about 0.45% carbon, about 1.3% to about 1.6% manganese, about 0.2% to about 0.4% silicon, about 1% to about 1.5% nickel, about 0.8% to about 1.2% chromium, about 0.25% to about 0.35 molybdenum, vanadium in an amount up to 0.1%,

and the balance essentially iron.

I References Cited in the file of this patent UNITED STATES PATENTS 2,327,490 Bagsar Aug. 24, 1943 2,379,988 Post et a1. July 10, 1945 2,565,953 Gaspari et al. .Aug. 28, 1951 FOREIGN PATENTS 344,822 Great Britain Mar. 11, 1931 OTHER REFERENCES ASM Metals Handbook, 1948 ed., pages 466-7. Published by the American Society for Metals, Cleveland, Ohio.

Bullens: Steel and Its Heat Treatment, 5th edition, vol. III, pages 229-23 0. Published by John Wiley & Sons, Inc., New York, N.Y. 

